Codes and standards updates and discussions related to codes and standards
t R1
R2
Figure 2: Effective width at edge stiffener.
Figure 1: Corner radius.
A
merican Iron and Steel Institute (AISI) cold-formed steel design and construction standards are developed and maintained by the AISI Committee on Specifications for the Design of Cold-Formed Steel Structural Members and the AISI Committee on Framing Standards. The operation of both Committees follow the “Essential Requirements: Due process requirements for American National Standards” established by American National Standards Institute. All the standards developed by the Committees go through ANSI conducted public review and approval processes to become American National Standards (ANS). All AISI standards published in 2007 were either reaffirmed as the ANS or published as a new edition in 2012. A complete list of AISI standards and their status is given in Table 1. This article provides an overview of major technical changes and additions that were included in the AISI standards and supplements published in 2012. 1) Technical Changes and Additions in AISI S100, North American Specification for the Design of Cold-Formed Steel Structural Members, 2012 Edition a) Section A2, Material. To facilitate the selection of appropriate steel grades, in the 2012 edition, the list of applicable steels has been grouped by their minimum elongation requirements over a two-inch (50-mm) gage length: the specified minimum elongation of 10 percent or greater, 3 percent to less than 10 percent, and less than 3 percent. The permitted uses and restrictions are then specified for each of the groups. For example, the steels with a specified minimum elongation of 10 percent or greater can be used without restriction as long as the steels meet the requirements specified in Section A2.3.1. Steels with elongation from 3 percent to 10 percent can be used with reduced yield stress and tensile strength as specified in Section A2.3.2. Steels with specified minimum less than 3 percent may be
Update: Cold-Formed Steel Design 2012 By Helen Chen Ph.D, P.E., LEED AP-BD+C, Roger L. Brockenbrough, P.E. and Richard B. Haws, P.E.
14 August 2013
used in multiple web configurations such as roofing, siding and floor decking provided the adjustments specified in Section A2.3.3 are met. Additionally, a new material standard ASTM A1063/ A1063M, Standard Specification for Steel Sheet, Twin Roll Cast, Zinc-coated (Galvanized) by the Hot-Dip Process, was added in 2012. b) Section B1.3, Corner Radius-toThickness Ratios. Research indicated that the provisions in Chapter B may become unconservative when predicting the effective width if the corner radiusto-thickness ratio, R/t, is larger than 10 (Figure 1). Thus, the effective width equations in Chapter B are restricted to R/t less than or equal to 10. However, the design engineer may use crosssections having radius-to-thickness ratios greater than 10 by using a rational engineering analysis method such as the Direct Strength Method or a prescriptive method applicable for 10 < R/t ≤ 20 that is provided in AISI S100 Commentary Section B1.3. c) Section B2.5, Uniformly Compressed Elements Restrained by Intermittent Connections. This section is used to determine the effective widths for elements, such as cellular decks, that are restrained by intermittent connections (Figure 2). The added provisions will enable increased moment capacities for some cellular deck profiles. d) Section C3.6, Combined Bending and Torsional Loading. This section takes into consideration the torsional effect for singly or doubly symmetric section members subjected to bending and torsional loading by applying a reduction factor, R, to the nominal flexural strength determined based on initial yielding. The reduction factor, R, was revised in 2012: R=
fbending_max ≤ 1 Eq. (1) fbending + ftorsion
where fbending_max = Bending stress at extreme fiber, taken on the same side of the neutral axis as fbending, fbending = Bending stress at location in cross-section where
